Blended wing body aircraft

ABSTRACT

A blended wing body aircraft having an interior cabin with a usable volume of at most 4500 ft 3  and a cabin aspect ratio of at most 4, wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.7 and at most 2.8. Also, a blended wing body aircraft having an interior cabin with a usable volume of at least 1500 ft 3  and at most 4500 ft 3  and a cabin aspect ratio of at least 2 and at most 4, wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.9 and at most 2.7. Also, a blended wing body aircraft wherein at least each profile section having normalized half-span values from 0 to 0.3 has a leading edge having a normalized height having a nominal value within the range set forth in Table 4.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional application No. 62/264,996 filed Dec. 9, 2015 and U.S. provisional application No. 62/291,273 filed Feb. 4, 2016, the entire contents of both of which are incorporated by reference herein.

TECHNICAL FIELD

The application relates generally to aircraft profiles and, more particularly, to the profile of a blended wing body aircraft.

BACKGROUND OF THE ART

A number of blended wing body designs are known, but such are typically designed for relatively large aircraft, for example seating 200 people or more. Such designs cannot simply be scaled down for smaller aircraft, as the resulting height would not be suitable to accommodate passengers.

Typical blended wing body aircraft have a relatively large wetted area, which may impede aerodynamic efficiency.

SUMMARY

In one aspect, there is provided a blended wing body aircraft comprising: an airfoil shaped center body including an interior cabin having a usable volume of at most 4500 ft³, the interior cabin having a maximum length defined along a longitudinal centerline of the center body and a maximum width defined perpendicularly to the maximum length, a cabin aspect ratio of the maximum length to the maximum width being at most 4; and a pair of wings extending from opposed sides of the center body; wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.7 and at most 2.8, wherein the wetted aspect ratio is defined by b²/S_(wet), where b is a maximum span of the wings measured without considering wing tip devices, and S_(wet) is a wetted area of the combination of the wings and center body.

This blended wing body aircraft may have any of the following characteristics, or any combination of the following characteristics:

-   -   the usable volume of the interior cabin is at least 1500 ft³;     -   the usable volume is at least 2000 ft³ and at most 4000 ft³;     -   the cabin aspect ratio is at least 2;     -   the cabin aspect ratio is at most 3.5;     -   the wetted aspect ratio of the combination of the wings and         center body is at least 1.9;     -   the wetted aspect ratio of the combination of the wings and         center body is least 2.1;     -   the wetted aspect ratio of the combination of the wings and         center body is about 2.4;     -   a ratio between a maximum thickness of the center body at the         longitudinal centerline and a length of a chord along the         longitudinal centerline has a nominal value of at least 16%;     -   a reference line is defined perpendicularly to a direction         defined by a maximum thickness of the center body at a mid-point         of the maximum thickness. The reference line extends fore-to-aft         in relation to the center body. A part of each of the wings has         a leading edge located a first distance below the reference         line, the first distance being measured along the direction         defined by the maximum thickness and corresponding to at least         10% of the maximum thickness;     -   the part of the wings having a leading edge located a first         distance below the reference line extends laterally from the         center body to a second distance from the centerline measured         along a span direction of the wings, the second distance         corresponding to at least 40% of a maximum half-span length of         the aircraft, the maximum half-span length defined along the         span direction from the centerline to a tip of one of the wings;         and/or     -   a part of each of the wings has a leading edge located below the         reference line at a distance measured along the direction         defined by the maximum thickness and corresponding to at least         15% of the maximum thickness.

In another aspect, there is provided a blended wing body aircraft comprising an airfoil shaped center body including an interior cabin having a usable volume of at least 1500 ft³ and at most 4500 ft³, the interior cabin having a maximum length defined along a longitudinal axis of the center body and a maximum width defined perpendicularly to the maximum length, a cabin aspect ratio of the maximum length to the maximum width being at least 2 and at most 4; a pair of wings extending from opposed sides of the center body; wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.9 and at most 2.7, wherein the wetted aspect ratio is defined by b²/S_(wet), where b is a maximum span of the wings measured without considering wing tip devices, and S_(wet) is a wetted area of the combination of the wings and center body.

This blended wing body aircraft may have any of the following characteristics, or any combination of the following characteristics:

-   -   the cabin aspect ratio is at most 3.5;     -   the usable volume of the interior cabin is at least 2000 ft³ and         at most 4000 ft³;     -   the wetted aspect ratio of the combination of the wings and         center body is at least 2.1;     -   the wetted aspect ratio of the combination of the wings and         center body is about 2.4;     -   a ratio between a maximum thickness of the center body at the         longitudinal centerline and a length of a chord along the         longitudinal centerline has a nominal value of at least 16%;     -   a reference line is defined perpendicularly to a direction         defined by a maximum thickness of the center body at a mid-point         of the maximum thickness. The reference line extends fore-to-aft         in relation to the center body. A part of each of the wings has         a leading edge located a first distance below the reference         line, the first distance being measured along the direction         defined by the maximum thickness and corresponding to at least         10% of the maximum thickness; and/or     -   the aircraft has a span direction, and a maximum half-span         length defined along the span direction from a centerline of the         center body to a tip of one of the wings. A normalized half-span         value for each profile section of the aircraft is defined by a         ratio between a distance along the span direction from the         centerline to the profile section, and the maximum half-span         length. A reference line is defined perpendicularly to a         direction defined by a maximum thickness of the center body at a         mid-point of the maximum thickness, the reference line extending         fore-to-aft in relation to the center body. Each profile section         of the aircraft has a leading edge having a normalized height         with respect to the reference line, the normalized height         corresponding to a ratio of a distance from the reference line         being measured along the direction defined by the maximum         thickness to the maximum thickness. The normalized height has a         nominal value within the leading edge normalized height range         set forth in Table 4 for at least each profile section         corresponding to the normalized half-span values from 0 to 0.3.

In another aspect, there is provided a blended wing body aircraft comprising: an airfoil shaped center body; and a pair of wings extending from opposed sides of the center body; wherein the aircraft has a span direction, and a maximum half-span length defined along the span direction from a centerline of the center body to a tip of one of the wings; wherein a normalized half-span value for each profile section of the aircraft is defined by a ratio between a distance along the span direction from the centerline to the profile section, and the maximum half-span length; wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body; wherein each profile section of the aircraft has a leading edge having a normalized height with respect to the reference line, the normalized height corresponding to a ratio of a distance from the reference line being measured along the direction defined by the maximum thickness to the maximum thickness, the normalized height having a nominal value within the leading edge normalized height range set forth in Table 4 for at least each profile section corresponding to the normalized half-span values from 0 to 0.3.

This blended wing body aircraft may have any of the following characteristics, or any combination of the following characteristics:

-   -   the nominal value of the leading edge normalized height is         within the leading edge normalized height range set forth in         Table 4 for at least each profile section corresponding to the         normalized half-span values from 0 to 0.4;     -   the nominal value of the leading edge normalized height is         within the leading edge normalized height range set forth in         Table 5 for at least each profile section corresponding to the         normalized half-span values from 0 to 0.3; and/or     -   the nominal value of the leading edge normalized height is         within the leading edge normalized height range set forth in         Table 5 for at least each profile section corresponding to the         normalized half-span values from 0 to 0.4.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic isometric view of a blended wing aircraft according to a particular embodiment;

FIG. 2 is a schematic top view of wetted surfaces of the aircraft of FIG. 1, in accordance with a particular embodiment;

FIG. 3 is a schematic front view of the wetted surfaces of FIG. 2;

FIG. 4 a schematic top cross-sectional view of a cabin of the aircraft of FIG. 1, in accordance with a particular embodiment;

FIG. 5 is a graph showing examples of normalized chord distribution as a function of normalized half-span for the aircraft of FIG. 1, in accordance with particular embodiments;

FIG. 6 is an enlarged portion of the graph of FIG. 5;

FIG. 7 is a graph showing examples of thickness ratio distribution as a function of normalized half-span for the aircraft of FIG. 1, in accordance with particular embodiments;

FIG. 8 is an enlarged portion of the graph of FIG. 7;

FIG. 9 is a graph showing an example of normalized leading edge height distribution as a function of normalized half-span for the aircraft of FIG. 1, in accordance with a particular embodiment; and

FIG. 10 is a schematic side view of three different profile sections of the aircraft, illustrating the normalized leading edge height shown by FIG. 9.

DETAILED DESCRIPTION

In the present specification, including claims, it is understood that a range of values formulated as “from X to Y” is inclusive, i.e. includes the values X and Y.

Blended wing body designs are sometimes also referred to as “hybrid wing body” designs. In the present specification, including claims, it is understood that the term “blended wing body” encompasses designs which are sometime referred to as “hybrid wing body” designs.

Referring to the drawings and more particularly to FIG. 1, a blended wing body aircraft is shown at 10. The aircraft 10 has a center body 12 having a fore end at which a cockpit is located, and an opposed aft end. The center body 12 is airfoil-shaped such as to be able to generate lift. In the embodiment shown, the aircraft 10 is tailless; alternately, a tail structure may be provided at the aft end of the center body 12 and/or a canard may be provided at the fore end of the center body 12. Wings 14 project laterally from opposite sides of the center body 12. The aircraft 10 has engines 16 mounted to the aft end of the center body 12; alternately, the engines 16 could be mounted on the wings 14 or they could be fully or partially embedded within the center body 12 or the wings 14. The aircraft 10 is shown as a jet-engine aircraft, but may also be a propeller aircraft.

Referring to FIG. 4, the center body 12 includes an interior cabin 18 for receiving payload, for example passengers. As used herein, the term “passengers” includes both crew and non-crew individuals located on-board the aircraft 10. In addition, the term “passengers” includes both civilian and military travellers. The cabin 18 has a maximum length L defined along a longitudinal centerline 20 of the center body 12 and a maximum width W defined perpendicularly to the maximum length. The blended wing body shape allows for the center body 12 to have a greater width than that of a tubular fuselage aircraft having a similar cabin volume, such as to be able to accommodate for example two or more aisles of passenger seating or two side-by-side sections as per the exemplary embodiment shown.

The cabin 18 has a usable volume which is defined as the sum of stand-up volume and additional volume situated above the cabin floor, excluding the pilot compartment. The stand-up volume is defined as the volume having a flat floor and at least a predetermined height. In a particular embodiment, the predetermined height is 72 inches or higher. In a particular embodiment, the additional volume has a minimum height of 50 inches at its lowest edges, and a gradient between the minimum height and the height of the stand-up volume of at least 0.73 inches in height per 1.0 inch of width. It is understood that the particular values provided are examples only and that other appropriate values may be used.

In a particular embodiment, the cabin 18 according to the present invention has a usable volume selected from the following values: at most 4500 ft³, at most 4000 ft³, from 1500 ft³ to 4000 ft³, from 1500 ft³ to 4500 ft³, from 2000 ft³ to 4000 ft³, and from 2000 ft³ to 4500 ft³; and the cabin aspect ratio, which is defined as the maximum length to the maximum width (L/W) of the cabin, is selected from the following values: at most 4, at most 3.5, from 2 to 4, and from 2 to 3.5. Blended wing body aircrafts with such cabin aspect ratios are typically designed with much larger cabin usable volumes, and their shape cannot simply be scaled down to a smaller volume because the resulting cabin height would be insufficient to accommodate passengers.

In a particular embodiment, the cabin 18 according to the present invention has a usable volume of approximately 2400 ft³, with a ratio of stand-up volume to total usable volume of at least 50%; in a particular embodiment, the ratio of stand-up volume to total usable volume is about 80%. Such a cabin preferably has a flat cabin floor area of at least 0.13 ft² per 1 ft³ of usable volume; in a particular embodiment, the flat cabin floor area is at least 0.15 ft² per 1 ft³ of usable volume. In a particular embodiment, these ratios of stand-up volume to total usable volume and/or these minimum ratios of flat floor area to usable volume may be applied to any of the cabin volumes mentioned above. On larger aircraft, the flat floor area could be arranged in multiple decks.

In a particular embodiment, the flat cabin floor has a pitch angle of at most 3.5 degrees in typical cruise flight condition or on ground excluding taxi, take-off and landing phases.

In a particular embodiment with an airline interior, the usable volume of the cabin is selected to accommodate from 50 to 70 passengers. In a particular embodiment, the usable volume of the airline cabin is selected to accommodate about 50 passengers. In a particular embodiment with a business aircraft interior, the usable volume of the cabin is selected to accommodate from 8 to 18 passengers. In a particular embodiment, the usable volume of the business aircraft cabin is selected to accommodate about 14 passengers.

The aircraft 10 is particularly shaped to be able to obtain the desired combination of cabin aspect ratio and usable volume while maintaining aerodynamic efficiency. The outer (wetted) surfaces of the aircraft are configured such as to reduce the wetted area with respect to more traditional blended wing body shapes; the reduction in wetted area reduces friction drag. The wetted area is reduced while simultaneously realizing induced drag and trim drag benefits and while aiming to maintain a wave drag comparable to or better than that of a conventional aircraft having a tubular fuselage.

Referring to FIGS. 2-3, in a particular embodiment the reduction of wetted area is achieved by a “carving out” of the leading edge 24 and trailing edge 26 in the transition zone 22 from the center body 12 to the wing 14, as compared to more traditional blended wing body shapes (an example of which is shown at 8 in dotted lines). Accordingly, the chord length (C) (FIG. 2) and thickness (t) (FIG. 3) of the aircraft 10 are reduced more aggressively upon transition from the center body 12 to the wings 14; the resulting profile defines a tridimensional shape which features a relatively voluminous lift-creating center body 12 which quickly transitions to wings 14 which may have a shape similar to that of wings of a conventional aircraft with a tubular fuselage. The relative thickness (height) at the cabin in relation to the wing thickness is larger than more traditional blended wing body shapes.

The reduced wetted area results in an increased wetted aspect ratio. The wetted aspect ratio of the combination of the wings 14 and center body 12 is defined as follows:

$\frac{b^{2}}{S_{wet}}$

where b is the maximum wing span measured without considering winglets and other wing tip devices, and S_(wet) is the wetted area of the combination of the wings 14 and center body 12. The wetted area is measured without taking into consideration elements added to the body 12 and/or wings 14, such as winglets, engine nacelles, pylons, etc.

In a particular embodiment, the combination of the wings 14 and center body 12 has a wetted aspect ratio selected from the following values: from 1.7 to 2.8; from 1.9 to 2.7; from 2.1 to 2.7; about 2.4.

In a particular embodiment, the aspect ratio of the combination of the wings 14 and center body 12, which is defined as

$\frac{b^{2}}{A}$

where A is the projected area of the combination of the wings 14 and center body 12, has a value selected from the following values: from 4.5 to 7.2; from 5.1 to 7.1; from 5.7 to 7.1; about 6.3.

In a particular embodiment, the aircraft 10 is configured for typical flight at Mach 0.85 with a capability to cruise at Mach 0.90. The aircraft 10 may alternately be configured for flight at other adequate speeds.

A shape or profile of the aircraft 10 in accordance with particular embodiments will be described herein. Although the parameters described are particularly suited for an aircraft having a usable volume as described above, it is understood that these parameters may also be used in aircraft having larger usable volumes; in sufficiently large usable volumes, the profile described may allow for a cabin height sufficient to create multiple levels, i.e. vertically superposed spaces for receiving passengers.

The aircraft 10 can be defined by profile sections which correspond to “slices” of the aircraft shape taken parallel to a longitudinal plane of symmetry P (see FIG. 3) of the center body 12; these slices reveal the airfoil profile of each section of the aircraft 10. Referring to FIG. 2, the position of each profile section with respect to the centerline 20 is defined by a normalized half span which corresponds to the ratio between a distance (d) from the centerline to that section measured along the direction of the span, and the maximum half-span length (b/2) of the aircraft 10 which is measured from the centerline 20 to the wing tip 28 (excluding winglet and other wing tip devices). The normalized half-span value

$\left( \frac{d}{b/2} \right)$

is expressed herein has a number varying from 0 (at the centerline 20) to 1.0 (at the wing tip 28), but could alternately be expressed as a % of the maximum half-span length.

Still referring to FIG. 2, each profile section of the aircraft 10 is characterized by a normalized chord which is defined by a ratio between the chord length (C) of that section and the maximum chord length (C_(MAX)) of the aircraft. The normalized chord value

$\left( \frac{C}{C_{MAX}} \right)$

is expressed herein as a % of the maximum chord length, but could alternately be expressed by a number having a maximum value of 1.0 (at the section defining the maximum chord length, typically at centerline 20).

Referring to FIG. 3, each profile section of the aircraft 10 is also characterized by a thickness ratio, which corresponds to a ratio between the corresponding thickness (t) and chord length (C) (FIG. 2) of that section. The thickness ratio value (t/C) is expressed herein as a % of the chord length, but could alternately be expressed by an equivalent numerical value (e.g. decimal number). The thickness (t) of each airfoil shape (center body, wings) is measured perpendicularly to its chord line.

FIGS. 5-6 show the normalized chord distribution as a function of the distance from the center line 20 as defined by the normalized half-span, and FIGS. 7-8 show the thickness ratio distribution as a function of the distance from the center line 20 as defined by the normalized half-span, for a few aircrafts 10 according to particular embodiments. Table 1 below sets forth value ranges for the normalized chord and the thickness ratio according to a particular embodiment, which encompass but are not limited to the distributions of FIGS. 5-8:

TABLE 1 Normalized thickness Normalized chord ratio half-span value range (%) range (%) (dimensionless) From To From To 0.000 100.0 100.0 15.2 19.4 0.050 85.4 100.0 15.0 19.4 0.100 58.0 96.0 14.5 19.2 0.125 44.5 92.0 12.2 19.0 0.150 31.0 78.5 9.8 18.7 0.175 26.0 65.0 9.0 18.2 0.200 23.0 51.0 8.7 16.5 0.250 20.0 34.0 8.3 11.8 0.300 17.9 28.0 8.1 11.3 0.350 17.0 24.5 8.0 11.1 0.400 16.0 23.2 8.0 11.0 0.500 14.2 21.3 8.0 10.9 0.600 12.5 19.5 8.0 10.9 0.700 10.7 17.5 8.0 10.9 0.800 9.0 15.7 8.0 10.9 0.900 7.3 13.9 8.0 10.9 1.000 5.5 12.0 8.0 10.9

Table 2 below sets forth smaller value ranges for the normalized chord and the thickness ratio according to another particular embodiment, which encompass at least some of the distributions of FIGS. 5-8:

TABLE 2 Normalized thickness Normalized chord ratio half-span value range (%) range (%) (dimensionless) From To From To 0.000 100.0 100.0 15.2 18.4 0.050 85.4 100.0 15.2 19.4 0.100 61.1 94.0 14.9 19.1 0.125 49.0 87.0 13.1 18.8 0.150 35.0 70.0 11.2 18.4 0.175 29.0 55.1 9.3 17.6 0.200 25.5 43.3 8.9 15.2 0.250 21.0 31.9 8.5 11.4 0.300 18.4 26.8 8.2 11.1 0.350 17.5 23.7 8.1 11.0 0.400 16.5 22.7 8.1 10.9 0.500 14.7 20.8 8.1 10.7 0.600 13.0 19.0 8.1 10.7 0.700 11.2 17.0 8.1 10.7 0.800 9.5 15.2 8.1 10.7 0.900 7.8 13.4 8.1 10.7 1.000 6.0 11.5 8.1 10.7

Table 3 below sets forth other smaller value ranges for the normalized chord and the thickness ratio according to another particular embodiment, which encompass at least some of the distributions of FIGS. 5-8:

TABLE 3 Normalized thickness Normalized chord ratio half-span value range (%) range (%) (dimensionless) From To From To 0.000 100.0 100.0 15.4 16.8 0.050 89.0 98.0 15.4 17.5 0.100 68.0 91.0 15.0 18.0 0.125 53.5 82.0 13.3 18.0 0.150 37.5 65.0 11.4 17.8 0.175 31.2 52.1 9.5 17.1 0.200 27.2 42.0 9.1 14.7 0.250 22.5 31.0 8.8 11.2 0.300 20.0 25.0 8.6 10.5 0.350 19.0 22.5 8.5 10.2 0.400 18.0 21.5 8.5 10.1 0.500 16.1 19.5 8.5 10.1 0.600 14.3 17.7 8.5 10.1 0.700 12.4 15.9 8.5 10.1 0.800 10.6 14.0 8.5 10.1 0.900 8.7 12.0 8.5 10.1 1.000 7.0 10.0 8.5 10.1

In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0.15 to 0.3; in a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0.15 to 0.5. In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 1 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 2 for at least the profile sections having normalized half-span values from 0.15 to 0.3; in a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 2 for at least the profile sections having normalized half-span values from 0.15 to 0.5. In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 2 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 3 for at least the profile sections having normalized half-span values from 0.15 to 0.3; in a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 3 for at least the profile sections having normalized half-span values from 0.15 to 0.5. In a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 3 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the nominal values for the normalized chord in the region defined by the normalized half-span values from 0.1 to 0.2 define a slope or rate of change selected from the following values: at least −3.5; at least −4.3; from −3.5 to −4.3; from −3.5 to −5.1; from −4.3 to −5.1. In addition or alternately, the nominal values for the normalized chord in the overlapping region defined by the normalized half-span values from 0.1 to 0.3 define a slope or rate of change selected from the following values: at least −2.4; at least −2.8; from −2.4 to −2.8; from −2.4 to −3.2; from −2.8 to −3.2. It is understood that the expression “at least” refers to the absolute value of the rate of change, i.e. to include greater rates of changes; in the case of a negative value (reduction), “at least −3.5” includes negative rates having a greater absolute value such as for example −3.6, −4.0, etc. The rate of change corresponds to the dimensionless ratio of the variation in normalized chord to the variation in normalized span; for example, a rate of change of −3.5 corresponds to a reduction of 35% in the normalized chord value over a region of 0.1 (10%) normalized span. The normalized chord distribution corresponding to any of these slopes or rates of change may follow part of Table 1, Table 2 or Table 3, the whole of Table 1, Table 2 or Table 3, or be different from Table 1, Table 2 and Table 3.

In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0 to 0.2; in a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0 to 0.3. In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 1 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 2 for at least the profile sections having normalized half-span values from 0 to 0.2; in a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 2 for at least the profile sections having normalized half-span values from 0 to 0.3. In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 2 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 3 for at least the profile sections having normalized half-span values from 0 to 0.2; in a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 3 for at least the profile sections having normalized half-span values from 0 to 0.3. In a particular embodiment, the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 3 for the entire aircraft (i.e. normalized half-span from 0 to 1.0).

In a particular embodiment, the nominal values for the thickness ratio in the region defined by the normalized half-span values from 0.1 to 0.2 define a slope or rate of change selected from the following values: at least −0.27; at least −0.49; from −0.27 to −0.49; from −0.27 to −0.72; from −0.49 to −0.72. In addition or alternately, the nominal values for the thickness ratio in the overlapping region defined by the normalized half-span values from 0.1 to 0.3 define a slope or rate of change selected from the following values: at least −0.28; at least −0.37; from −0.28 to −0.37; from −0.28 to −0.45; from −0.37 to −0.45. It is understood that the expression “at least” refers to the absolute value of the rate of change, i.e. to include greater rates of changes; in the case of a negative value (reduction), “at least −0.28” includes negative rates having a greater absolute value such as for example −0.3, −0.4, etc.

The rate of change corresponds to the dimensionless ratio of the variation in thickness ratio to the variation in normalized span; for example, a rate of change of −0.28 corresponds to a reduction of 2.8% in the thickness ratio value over a region of 0.1 (10%) normalized span. The thickness ratio distribution corresponding to any of these slopes or rates of change may follow part of Table 1, Table 2 or Table 3, the whole of Table 1, Table 2 or Table 3, or be different from Table 1, Table 2 and Table 3.

In a particular embodiment, the thickness ratio at the centerline 20 has a nominal value of at least 16%; the remainder of the thickness ratio distribution may follow part of Table 1, Table 2 or Table 3, the whole of Table 1, Table 2 or Table 3, or be different from Table 1, Table 2 and Table 3. This may be combined with the normalized chords having nominal values within the normalized chord ranges set forth in Table 1, Table 2 or Table 3 for any of the ranges of normalized half-span mentioned above, for example for at least the profile sections having normalized half-span values from 0.15 to 0.3, or from 0.15 to 0.5, or for from 0 to 1.0.

It is understood that any nominal value and/or rate of change for the normalized chords mentioned above may be combined with any nominal value and/or rate of change for the thickness ratios mentioned above. For example, in a particular embodiment, the normalized chords have nominal values within the normalized chord ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0.15 to 0.3 and the thickness ratios have nominal values within the thickness ratio ranges set forth in Table 1 for at least the profile sections having normalized half-span values from 0 to 0.2. All other possible combinations may also be used.

Referring to FIGS. 9-10, in a particular embodiment, the wings 14 have a low position on the center body 12; this may help maximize the available flat floor area in the cabin. FIG. 9 shows an example of the distribution of the normalized height of the leading edge 24 as a function of the normalized half-span. FIG. 10 illustrates how the normalized height of the leading edge 24 is measured.

As can be seen from FIG. 10, the maximum thickness (t_(MAX)), or height, of the center body 12 is defined by the profile section 10° of the longitudinal centerline, i.e. at the normalized half-span value of 0. A mid-point reference line 30 extending in the plane of the profile, fore-to-aft in relation to the center body 12, can be defined perpendicularly to the direction 36 defined by the maximum thickness (t_(MAX)) at a mid-point of the maximum thickness, i.e. at mid distance between opposed top and bottom surfaces 32, 34 of the center body 12 where the maximum thickness is defined. The vertical position or height of elements of the aircraft 10 may be indicated with respect to this mid-point reference line 30, by their distance measured along the direction 36 defined by the maximum thickness, within the plane of each profile section. This distance may be indicated in terms of a % of the maximum thickness of the center body, i.e. as a ratio of the distance to the maximum thickness. Accordingly, the center body 12, at the centerline 20 (normalized half-span value of 0), has a normalized height extending between 50% and −50% of the maximum thickness. FIG. 10 also illustrates the profile section 10^(0.3) located at the normalized half-span value of 0.3 and the profile section 10^(1.0) located at the normalized half-span value of 1.0, to illustrate the evolution of the normalized height of the leading edge 24 along the span direction.

Referring back to FIG. 9, the distribution of the normalized height of the leading edge 24 in accordance with a particular embodiment is shown. The normalized height of the leading edge 24 of the profile section at each normalized half-span value (wing 14 or center body 12) is indicated in reference to the mid-point reference line 30, as a % of the maximum thickness of the center body 12. It can be seen that a significant part of the leading edge 24 is located at a distance of at least 10% of the maximum thickness below the mid-point reference line 30. In some of the embodiment shown, the leading edge 24 remains at a distance of at least 10% of the maximum thickness below the mid-point reference line 30 from the centerline 20 to a normalized half-span value of at least 0.3 (or 30%). Table 4 below sets forth value ranges for the normalized height of the leading edge 24 according to a particular embodiment, which encompass but are not limited to the distributions of FIG. 9:

TABLE 4 Leading edge normalized Normalized height half-span value range (%) (dimensionless) From To 0.00 3.0 −17.0 0.05 2.0 −18.0 0.10 1.0 −21.0 0.15 −1.0 −24.0 0.20 −2.0 −27.0 0.25 −3.0 −30.0 0.30 −3.0 −30.0 0.35 −2.0 −30.0 0.40 −1.0 −27.0 0.45 0.0 −24.0

Table 5 below sets forth smaller value ranges for the normalized height of the leading edge 24 according to another particular embodiment, which encompass at least some of the distributions of FIG. 9:

TABLE 5 Leading edge normalized Normalized height half-span value range (%) (dimensionless) From To 0.00 1.0 −15.0 0.05 0.0 −16.0 0.10 −1.0 −19.0 0.15 −3.0 −22.0 0.20 −5.0 −25.0 0.25 −6.0 −26.0 0.30 −6.0 −26.0 0.35 −5.0 −24.0 0.40 −3.0 −22.0 0.45 −1.0 −20.0

In a particular embodiment, the normalized heights of the leading edges 24 have nominal values within the leading edge normalized height ranges set forth in Table 4 for at least the profile sections having normalized half-span values from 0 to 0.3; in a particular embodiment, the normalized heights of the leading edges 24 have nominal values within the leading edge normalized height ranges set forth in Table 4 for at least the profile sections having normalized half-span values from 0 to 0.4. In a particular embodiment, the normalized heights of the leading edge 24 have nominal values within the leading edge normalized height ranges set forth in Table 4 for the entire table (i.e. normalized half-span from 0 to 0.45).

In a particular embodiment, the normalized heights of the leading edges 24 have nominal values within the leading edge normalized height ranges set forth in Table 5 for at least the profile sections having normalized half-span values from 0 to 0.3; in a particular embodiment, the normalized heights of the leading edges 24 have nominal values within the leading edge normalized height ranges set forth in Table 5 for at least the profile sections having normalized half-span values from 0 to 0.4. In a particular embodiment, the normalized heights of the leading edge 24 have nominal values within the leading edge normalized height ranges set forth in Table 5 for the entire table (i.e. normalized half-span from 0 to 0.45).

In a particular embodiment, the wing position shown helps obtain a sufficient flat floor area in the cabin, while minimizing the operational and design impacts of having a low wing position.

It is understood that alternate normalized heights for the leading edge 24 are possible, and that the values are provided as an example only.

In a particular embodiment, the aircraft profile discussed herein allows for improved fuel efficiency, emissions, operating costs, external storage capacity and/or noise management when compared to a tubular aircraft having a similar cabin usable volume. The blended wing body shape additionally allows for new seat and cabin design configurations within a relatively small cabin usable volume.

In a particular embodiment, the shape of the center body allows to approach the ideal elliptical lift distribution with respect to the minimization of drag forces. Significant drag reduction may allow for fuel burn reduction which can lead to savings in operating costs and may help achieve design weight reduction, which in turn may lead to a need for smaller engines and other systems.

It is understood that any combination or sub-combination of the elements of the different embodiments is within the scope of this disclosure. While the methods and systems described herein have been described and shown with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, sub-divided or reordered to form an equivalent method without departing from the teachings of the present invention. Accordingly, the order and grouping of the steps is not a limitation of the present invention.

Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims. 

1. A blended wing body aircraft comprising: an airfoil shaped center body including an interior cabin having a usable volume of at most 4500 ft³, the interior cabin having a maximum length defined along a longitudinal centerline of the center body and a maximum width defined perpendicularly to the maximum length, a cabin aspect ratio of the maximum length to the maximum width being at most 4; and a pair of wings extending from opposed sides of the center body; wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.7 and at most 2.8, wherein the wetted aspect ratio is defined by $\frac{b^{2}}{S_{wet}},$ where b is a maximum span of the wings measured without considering wing tip devices, and S_(wet) is a wetted area of the combination of the wings and center body.
 2. The blended wing body aircraft according to claim 1, wherein the usable volume of the interior cabin is at least 1500 ft³.
 3. The blended wing body aircraft according to claim 1, wherein the usable volume of the interior cabin is at least 2000 ft³ and at most 4000 ft³.
 4. The blended wing body aircraft according to claim 1, wherein the cabin aspect ratio is at least
 2. 5. The blended wing body aircraft according to claim 1, wherein the cabin aspect ratio is at most 3.5.
 6. The blended wing body aircraft according to claim 1, wherein the wetted aspect ratio of the combination of the wings and center body is at least 1.9.
 7. The blended wing body aircraft according to claim 1, wherein the wetted aspect ratio of the combination of the wings and center body is at least 2.1.
 8. The blended wing body aircraft according to claim 1, wherein the wetted aspect ratio of the combination of the wings and center body is about 2.4.
 9. The blended wing body aircraft according to claim 1, wherein a ratio between a maximum thickness of the center body at the longitudinal centerline and a length of a chord along the longitudinal centerline has a nominal value of at least 16%.
 10. The blended wing body aircraft according to claim 1, wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body, a part of each of the wings having a leading edge located a first distance below the reference line, the first distance being measured along the direction defined by the maximum thickness and corresponding to at least 10% of the maximum thickness.
 11. The blended wing body aircraft according to claim 1, wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body, a part of each of the wings having a leading edge located a first distance below the reference line, the first distance being measured along the direction defined by the maximum thickness and corresponding to at least 15% of the maximum thickness.
 12. The blended wing body aircraft according to claim 10 wherein the part of the wings extends laterally from the center body to a second distance from the centerline measured along a span direction of the wings, the second distance corresponding to at least 40% of a maximum half-span length of the aircraft, the maximum half-span length defined along the span direction from the centerline to a tip of one of the wings.
 13. A blended wing body aircraft comprising: an airfoil shaped center body including an interior cabin having a usable volume of at least 1500 ft³ and at most 4500 ft³, the interior cabin having a maximum length defined along a longitudinal axis of the center body and a maximum width defined perpendicularly to the maximum length, a cabin aspect ratio of the maximum length to the maximum width being at least 2 and at most 4; a pair of wings extending from opposed sides of the center body; wherein a combination of the wings and center body has a wetted aspect ratio of at least 1.9 and at most 2.7, wherein the wetted aspect ratio is defined by $\frac{b^{2}}{S_{wet}},$ where b is a maximum span of the wings measured without considering wing tip devices, and S_(wet) is a wetted area of the combination of the wings and center body.
 14. The blended wing body aircraft according to claim 13, wherein the cabin aspect ratio is at most 3.5.
 15. The blended wing body aircraft according to claim 13, wherein the usable volume of the interior cabin is at least 2000 ft³ and at most 4000 ft³.
 16. The blended wing body aircraft according to claim 13, wherein the wetted aspect ratio of the combination of the wings and center body is at least 2.1.
 17. The blended wing body aircraft according to claim 13, wherein the wetted aspect ratio of the combination of the wings and center body is about 2.4.
 18. The blended wing body aircraft according to claim 13, wherein a ratio between a maximum thickness of the center body at the longitudinal centerline and a length of a chord along the longitudinal centerline has a nominal value of at least 16%.
 19. The blended wing body aircraft according to claim 13, wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body, a part of each of the wings having a leading edge located a first distance below the reference line, the first distance being measured along the direction defined by the maximum thickness and corresponding to at least 10% of the maximum thickness.
 20. The blended wing body aircraft according to claim 13, wherein: the aircraft has a span direction, and a maximum half-span length defined along the span direction from a centerline of the center body to a tip of one of the wings; wherein a normalized half-span value for each profile section of the aircraft is defined by a ratio between a distance along the span direction from the centerline to the profile section, and the maximum half-span length; wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body; and wherein each profile section of the aircraft has a leading edge having a normalized height with respect to the reference line, the normalized height corresponding to a ratio of a distance from the reference line being measured along the direction defined by the maximum thickness to the maximum thickness, the normalized height having a nominal value within the leading edge normalized height range set forth in Table 4 for at least each profile section corresponding to the normalized half-span values from 0 to 0.3.
 21. A blended wing body aircraft comprising: an airfoil shaped center body; and a pair of wings extending from opposed sides of the center body; wherein the aircraft has a span direction, and a maximum half-span length defined along the span direction from a centerline of the center body to a tip of one of the wings; wherein a normalized half-span value for each profile section of the aircraft is defined by a ratio between a distance along the span direction from the centerline to the profile section, and the maximum half-span length; wherein a reference line is defined perpendicularly to a direction defined by a maximum thickness of the center body at a mid-point of the maximum thickness, the reference line extending fore-to-aft in relation to the center body; wherein each profile section of the aircraft has a leading edge having a normalized height with respect to the reference line, the normalized height corresponding to a ratio of a distance from the reference line being measured along the direction defined by the maximum thickness to the maximum thickness, the normalized height having a nominal value within the leading edge normalized height range set forth in Table 4 for at least each profile section corresponding to the normalized half-span values from 0 to 0.3.
 22. The blended wing body aircraft according to claim 21, wherein the nominal value of the leading edge normalized height is within the leading edge normalized height range set forth in Table 4 for at least each profile section corresponding to the normalized half-span values from 0 to 0.4.
 23. The blended wing body aircraft according to claim 21, wherein the nominal value of the leading edge normalized height is within the leading edge normalized height range set forth in Table 5 for at least each profile section corresponding to the normalized half-span values from 0 to 0.3.
 24. The blended wing body aircraft according to claim 21, wherein the nominal value of the leading edge normalized height is within the leading edge normalized height range set forth in Table 5 for at least each profile section corresponding to the normalized half-span values from 0 to 0.4. 